The hard disk was probably the better route to go, IMO. Sure, you can back up as many discs of MP3's as you want, but you'll take up dozens of discs (as you said), which would make it less convenient than the CDs to begin with (you have to find which disk your song is on). Plus, unless you want to spend lots of money on rewriteable disks, you've got a static collection on your hands.

The 120 HDD was a better idea.